Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index a664996..57e545b 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -424,7 +424,7 @@
 	clear_page(page);
 
 	/*
-	 * We shouldnt have to do this, but some versions of glibc
+	 * We shouldn't have to do this, but some versions of glibc
 	 * require it (ld.so assumes zero filled pages are icache clean)
 	 * - Anton
 	 */